1. Field of the Invention
This invention relates to methods and devices intended to provide protection in electrical power or power extension cords from fire and other hazards associated with cord deterioration which may be caused by age and/or excessive heat, or by physical damage such as may be caused by kinking or crushing.
2. Background Information
Various means have been employed to provide protection against hazards associated with damage to power cord sets included with electrically energized devices and the power extension cords or cables made to extend their length. Devices such as GFCI's (Ground Fault Circuit Interrupters) have provided personnel protection against lethal shock due to a leakage from the ungrounded conductor that may pass through the body to a source of external grounding. Arcing fault detectors can provide some protection against the heat producing faults, which pass current between conductors enclosed by the cord structure that often cause fire, but depend on leakage fault escalation to the level of arcing to make the fault detectable. Incorporation of most protective devices involves an additional cost that tends to keep them from being widely used in a competitive market unless legally mandated.
Conventionally shielded power cords or cables offer a special opportunity for protection. Power cords or extensions have their conductors surrounded by a conductive shield in order to block emission and/or reception of radio frequencies and are primarily used in cords to provide power to high quality audio devices, computers, monitors, scanners and other sensitive equipment that might suffer from RF interference. Frequently employed shielding elements include conductive polymers, metallic foils or braids either singly or in combination. The present invention expands the use of this RF shield to create a protection against the fire hazard effect of low level leakages from the ungrounded conductor, too small to warrant the activation of service breakers, but large enough to cause deterioration of insulative materials, at minimal additional cost. While a grounded neutral and a grounding conductor are also present in the standard cord assembly, they are slender conduction targets in the matter of leakage due to damage. The greater area of the encompassing shield is readily available and offers a far more immediate pathway to ground, in the event of cord damage. However, the invention also calls for individualized shielding of the conductors for use with the conventional outer shield or without it, according to desired effect.